Dry South Florida Salutes Rainy Season

May 22, 2009|By David Zierden and James J. O'Brien

The last week of March and first week of April brought a shift in the large-scale weather patterns across the southeastern United States, characterized by an active jet stream with frequent low pressure systems moving across the northern Gulf Coast. Several of these systems were slow moving, allowing widespread rains and thunderstorms to dump heavy accumulations of rain over the two-week period across most of Georgia, Alabama and North Florida.

Unfortunately, these torrential rains failed to progress down the peninsula where the driest areas of the state are located. South of a diagonal line from Gainesville to St. Augustine, the peninsula received only one to two inches during the month of March and continued the string of months with below-normal rainfall. With winter rainfall deficits from five to 10 inches, drought continues to worsen across Central and South Florida.

According to the U. S. Drought Monitor, most of the peninsula is now classified as being in moderate or severe drought. Wildfire risk is also high in Central and South Florida, where the Keetch-Byram Drought Index is currently running from 600 to over 700, corresponding to extreme dryness.

Fortunately, the latter half of May and June bring the beginning of the rainy season, characterized by frequent afternoon thundershowers. In fact, the peninsula of Florida receives more than 40 percent of its yearly rainfall in the months of June-September. These showers moisten soils and green up the vegetation, greatly diminishing drought concerns and wildfire threats.

Historically, Florida has always been noted for warm, dry winters that lead to wet summers. As residents of this beautiful state, we are well aware that our warm, dry winters provide a favorable climate for a wide range of activities, from agriculture to tourism at our beaches and theme parks. Warm and humid summers produce rains that generate lush plant life for our homes and farms. The afternoon rains we are so accustomed to take the form of frequent thundershowers, which typically begin later in May over South Florida and spread up the state in early June. But what should bring comfort to us as Floridians is that our climate, our long-term weather history, is steeped in a pattern of dry winters and rain-filled summers.

David Zierden is a state climatologist for Florida, and James J. O'Brien is a meteorology and oceanography professor at Florida State University.